It is well known that the majority of energy intensive processes are driven by the rates of the heat and mass transfer. Specific details of a particular application, such as the chemistry of a substrate to be dried (e.g., a factor in label printing, sheet-fed and continuous printing, converting, packaging, mass mailing), the temperature of a material being applied, the needed residence time for a coating to dry, and water or solvent evaporation rates, are necessary for a drying and heating process to work properly. These factors dictate the size of the drying equipment.
It is also well known that the main thing that prevents an increase in heating and drying rates is the boundary layer that is formed around the subject or material to be heated or dried. In modern heating and drying practice there are several methods to disrupt the boundary layer. The most common method is to add hot convection air to other heating methods, such as, for example, radiant heating.
With convective heat, high-velocity impinging jets of hot air are directed onto the material and, consequently, onto the boundary layer to agitate the boundary layer. Similarly, impinging hot-air jets are used in infrared-light heating. Applying a convective airflow or infrared light typically increases the heat transfer rate by about 10-25%. Thus, these approaches have provided some improvement in heat-transfer rates, but further improvements are needed.
There are also known efforts of using pulse combustion to establish pulsating heat jets and apply them onto a material in order to reduce the boundary layer. With pulse combustion jets, flame generates sound in the audible frequency range. The use of pulse combustion jets typically increases the heat transfer rate by about 200-500% (when making a comparison with the same steady-state velocities, Reynolds numbers, and temperatures). Thus, this approach has provided significant improvement in heat-transfer rates, but the pulse combustion equipment is large/space-consuming and costly to purchase and operate. Additionally, a variety of industries require more compact equipment, and combustion gases sometimes are not allowed in the process due to its chemical nature (food, paints, coatings, printing, concerns of explosives, building codes, needs for additional natural gas lines, its maintenance, etc.).
Accordingly, it can be seen that a need exists for improved drying technologies that produce significantly increased heat-transfer rates but that are cost-efficient to make and use and preferably have a smaller footprint and require less material. It is to the provision of solutions meeting this and other needs that the present invention is primarily directed.